This patch adds several functions for writing the exception
to the logs with a full backtrace, including the causes for the exception.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@1566 44740490-163a-0410-bde0-09ae8108e29a

Including the cause of the exception will make it simpler to trace
exceptions through the program.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@1565 44740490-163a-0410-bde0-09ae8108e29a

Make the SimpleSAML_Error_Exception class suitable for serialization by
making it _not_ serialize the trace variable in the Exception class.

Serializing the trace-variable is problematic because it contains the
parameters to all function calls. This can make the exception very big.
This can also make the exception unserializable, if one of the
parameters is unserializable.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@1563 44740490-163a-0410-bde0-09ae8108e29a

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@1551 44740490-163a-0410-bde0-09ae8108e29a